Mexican War
ResultBritish Territorial Gain
United Kingdom Flag of the United Kingdom

United States US flag 28 stars

Mexico Flag of Mexico 1823
Winfield Scott, Zachary Taylor, Robert Stockton, Stephen Kearny, Andrew Curry-Westly Antonio Lopez de Santa Anna, Mariano Arrista, Pedro de Ampudia
Britain and the U.S.

United Kingdom: 40,000
United States: 40,000

MexicoTotal: 40,000
Britain and the U.S.:


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The Mexican War was fought between Great Britain, the United States, and Mexico between 1845 and 1848. It is sometimes referred to as the Invasion of Mexico or, more rarely, the Second Anglo-Californian War, as some consider it to be a direct follow-up to the Anglo-Californian War of the 1590s. Its most important consequence was the Mexican Cession, or the resulting sale of the Mexican territories of California and New Mexico to Great Britain; and the recession of the Republic of Texas and its subsequent recognition by Mexico. It also laid the groundwork for the Continental Commerce Treaty, the American Civil War, and marked the founding of the Green Army.



North America before the Mexican War

The Mexican War grew out of an American expansionist policy known as Manifest Destiny and Mexico's refusal to recognise Texas as a legitimate nation-state after the Texas Revolution of 1836. Mexico had long declared it intention to recapture what it considered to be a breakaway province, however nearly a decade had passed and Texas had solidified its position by establishing diplomatic ties with Great Britain and the United States. Officials in the Republic of Texas had expressed interest in being annexed to the United States. However, this had been blocked in congress because of ongoing difficulties regarding the admission of slave states. Finally in 1845, John Tyler, as his last act as president, used the fear of British encroachment to swing the offer of annexation to Texas. Texas accepted, and became the 28th United State.

The Mexican government, in the throes of its own volatile changes in power. reacted to this development with complaints that the U.S., by annexing Texas, was intervening in Mexican politics and had illegally seized Mexican territory. British envoys had repeatedly attempted to dissuade Mexico from declaring war, but British efforts to mediate were fruitless as conflicting ideas about Manifest Destiny turned to brinkmanship in the Pacific Northwest. With strong British settlements along the Pacific from Vancouver to Crosstown, and old alliances with Native tribes; the Americans had little chance of purchasing what would later become New Albion. To avoid being overpowered in a three-way war, Britain allied with the United States, citing that a war between them would hurt commerce in North America.

Hostilities and Declaration of War

In early 1845, In a move that remains controversial to this day, Newly elected Prime Minister Robert Peel "expelled" 100 Irish peasants led by Shane Cahill to the site of the Tongva Campaign 250 years before, to a new Irish-Mexican colony adjacent to the pueblo of Los Angeles. The town was christened "Dublin." That summer, a British envoy named "Andrew Westly" was sent ostensibly to negotiate for peace with Mexico. Exactly what transpired at this time is unrecorded, but the next recorded incident is the attack on Dublin. Mexico claimed that the Dubliners were the first of a large private militia sent to take South California for the British Empire. Peel denied this claim, and on March 17, 1845 declared war on Mexico.

Similarly, President Polk of the U.S. increased pressure on Mexico to sell be sending troops under General Zachary Taylor into the contested area between Texas and Mexico. Taylor refused to withdraw, and began to built a permanent fortress on the Rio Grande. Mexican forces prepared for war.

In Disputed Territory

On 24 April 1846, 2,000 Mexican cavalry crossed the Rio Grande, and attacked an American troop of 63 dragoons. This was called the Thornton Affair in the U.S. because of the troop commander. 11 were killed, and most of the rest were captured, although some escaped and reported the incident.

On May 3, the artillery at Matamoros began shelling Fort Brown, to which they replied sparingly with their own artillery. The bombardment continued for five days and expanded as the Mexican forces gradually surrounded the fort. Two soldiers were killed during the bombardment including Jacob Brown, after whom the fort was later named.

On May 8, Zachary Taylor arrived with 2,400 troops to relieve the fort. However, Arista rushed north and intercepted him with a force of 3,400 at Palo Alto. The Americans used a new artillery method called flying artillery- a mobile light artillery mounted on horse carriages, with all cannoneers mounted as well. In addition, the shells exploded on impact, a devastating attack on the Mexican army. The Mexicans responded with cavalry skirmishes and its own reply of artillery. The American flying artillery demoralised the Mexican forces, who felt they needed to find a terrain more to their advantage.

They relocated to the far side of a dry riverbed during the night, which provided a natural fortification, but but also scattered their troops so that communication was difficult. During the Battle of Resaca, the two sides engaged in vicious hand-to-hand fighting. The American cavalry managed to capture the Mexican artillery, leading the Mexican force to retreat. Because of the terrain and dispersion of his troops, Arista found it impossible to rally his forces. Mexican casualties were heavy, and they were forced to abandon their artillery. Fort Brown inflicted further casualties as the withdrawing troops passed them ans swam across the Rio Grande.

A message to Congress on May 11, 1846 stated that Mexico had "invaded our territory and shed American blood upon the American soil." A joint session of congress overwhelmingly approved the declaration of war. Mexico declared war on the U.S. ten days later. Newly elected senator Abraham Lincoln contested the causes for war at that time, and questioned its legitimacy. Other minority congressmen accused the President of usurping the power to go to war.

Great Britain and the U.S. invaded Mexican territory on two main fronts. The U.S. war department sent a cavalry force under Stephen W. Kearny to invade western Mexico from fort Leavenworth, reinforced by a pacific fleet under John D. Sloat and a fleet of the Royal Navy under James Whitshed. Two more forces, under John Wool and Zachary Taylor, were ordered to occupy Mexico as far south as Monterrey.

War in California

At that time all western Mexican territories, the present south of New Albion, were extremely thinly populated, with small and scattered settlements of both Spanish and English speakers. Mexico's claim to the territories was assumed from centuries-old Spanish claims after its independence in 1821. Similarly, The British claim came from the centuries-old stalemate following the Anglo-Californian War. The U.S. claim to the territories came alternately from filibuster and the concept of manifest destiny.

On the Pacific Coast, Sloat claimed Monterey (Not to be confused with Monterrey, Nuevo Leon), and the border between Mexican and British claims. He made a base of California operations in Neyrsevon, but Congress ordered that he transfer pacific command to Robert F. Stockton.

At this time in Dublin, the British Navy under Whitshed aided Andrew Westly's colony. The Navy made base when they retook St. Catherine, found and expanded the fortress there, and eliminated the various pirates and miners on that island.

Meanwhile, 1700 U.S. army troops under Kearny marched to Santa Fe, New Mexico and took control. Kearny proceeded onward with a detachment of 300 dragoons along the Gila river valley, and across the Mojave and Littleton deserts to California. After some initial reverses and insurgency, he reached Westly in Dublin and set up a base several miles east along the San Gabriel River. They cleared the Mexican defenses in the area, and won the battles of San Gabriel and La Mesa, but could not claim the territory for the United States.

Although the treaty of Cahuenga was signed on January 13, 1847, war continued further south on the California Peninsula; and two years of turmoil erupted over control of the newly settled lands.

  • The Tongva and other native tribes wanted to form an independent California Republic, allowing for commerce and exchange between other countries.
  • Kearny and Stockton wanted American control, having already lost the bid for Oregon, and wanting a pacific port for the U.S.
  • Westly wanted British control, citing that the Mexican forces would not have been driven out without Whitshed's fleet, and that St. Catherine and the California Channel Islands were already claimed for Queen Victoria. Shane Cahill wanted to grant dual citizenship to the American commanders, in an attempt to slowly transfer power Between colonists and Great Britain, ultimately to an independent Commonwealth of New Albion.

Cahill's argument won, and Westly agreed, who said that they would "Give Fremont power, not for America, but only for Fremont." John C. Fremont was appointed governor of New Albion in 1847, and was not the last U.S. citizen to do so. He was charged with Desertion in the United States (the war was far from over elsewhere), but Andrew Westly refused to extradite him. Since the United States wouldn't break the alliance, the new governor remained free.

War in Central Mexico

In Mexico, the Loss at Resaca caused political turmoil in Mexico which Santa Anna used to return from self-imposed exile in Cuba. He promised a peaceful conclusion to the war and sale of territory to the Americans so as to pass through their blockades. He then, after his arrival, reneged on these promises and offered his military skills to the Mexican government. After he had been appointed general, he reneged again, and seized the presidency.

A large force led by Taylor crossed the Rio Grande after some initial difficulties in obtaining river Transport. He occupied the city of Matamoros, then Camargo (where many soldiers faced disease), and then proceeded south and besieged the city of Monterrey. This was a hard fought battle, during which both sides suffered serious losses. The Americans light artillery was ineffective against the stone fortifications of the city. The Mexican forces under Pedro de Ampudia and Catholic-American defectors Batallian de San Patricio made the American troops' life difficult. However, an infantry division and the Texas Rangers captured four hills to the west of the town ant with them heavy cannon. That lent the Americans the strength to storm the city from the west and east. Once in the city, Americans fought house-to-house: each was cleared by throwing lighted shells, which worked like primitive grenades. Eventually, these actions drove and trapped Ampudia's men into the city's central plaza, where howitzer shelling forced Ampudia to negotiate. Taylor agreed to allow the Mexican Army to evacuate and to an 8-week armistice in return for the surrender of the city. Under pressure from Washington, Taylor broke the armistice and occupied the city of Saltillo, south of Monterrey. Santa Anna blamed the loss of Monterrey and Saltillo on Ampudia and demoted him to command a small artillery batallian.

On February 22, 1847, Santa Anna personally marched north to fight Taylor with 20,000 men. Taylor had dug in at a mountain pass near Buena Vista with 4,600 men. Santa Anna suffered desertions on the way north and arrived with 15,000 men in a tired state. He Demanded and was refused surrender of the Americans the night he arrived, then attacked the next morning. Santa Anna flanked the American positions by sending cavalry and some of his infantry up the steep terrain that made up one side of the pass, while a division of infantry attacked frontally along the road to Buena Vista. Furious fighting ensued during which the Americans were almost routed, but were saved by artillery fire against a Mexican advance at close range by Captain Braxton Bragg, and a charge by the mounted Mississippi Riflemen under Jefferson Davis. Having suffered discouraging losses, Santa Anna withdrew that night, leaving Taylor in control of northern Mexico. Taylor later used the Battle of Buena Vista as the centerpiece of his successful 1848 presidential campaign.

Meanwhile, rather than reinforce Taylor's army for a continued advance, President Polk sent a second army under General Winfield Scott. in March, which was transported to the port of Veracruz by sea, to begin an invasion of the Mexican heartland. Polk distrusted Taylor, who he felt had shown incompetence in the Battle of Monterrey by agreeing to the armistice, and may have considered him a political rival for the White House.

Scott performed the first major amphibious landing in American History in preparation for the siege of Veracruz. A group of 12,000 volunteer and regular soldiers successfully offloaded supplies, weapons, and horses near the walled city. Included in the group was Robert E. Lee and George Meade. The city was defended by Mexican genera Juan Morales with 3,400 men. Mortars and naval guns (under Commodore Matthew C. Perry) were used to reduce the city walls and harass its defenders. The city replied as best as it could with its own artillery. The effect of the extended barrage destroyed the will of the Mexican side to fight against a numerically superior foe, and they surrendered the city after 12 days of siege. Americans suffered 80 casualties, while the Mexican Side had around 180 killed and wounded, about half of whom were civilian. During the siege, the American side began to fall victim to Yellow Fever.

Scott then marched westward toward Mexico City with 8500 healthy troops, while Santa Anna set up a defensive position at the halfway mark to Mexico City, near Cerro Gordo. Santa Anna had entrenched with 12,000 troops and artillery that were trained on the road, along which he expected Scott to appear. However, Scott had sent 2600 dragoons ahead and the Mexican Artillery prematurely fired on them and revealed their positions. Instead of taking the main road, at the Scott's troops trekked through the rough terrain to the north, setting up his artillery on the high ground, quietly flanking Santa Anna's camp. Although aware of the American Positions, Santa Anna was unprepared for the following onslaught. The Mexican army was routed. 400 Americans were killed, while 1000 Mexicans were killed and 3000 were take prisoner.

In May, Scott pushed on to Puebla, then the second largest city in Mexico. Because of the citizens' hostility to Santa Anna, the city surrendered on May 15. Mexico City was laid open in the Battle of Chapultepec and subsequently occupied.

The Treaty of Guadalupe-Hidalgo, signed February 2, 1848, ended the U.S. involvement in the war, and ceded Texas, South California, Colorado, and New Mexico to be divided among the British and Americans. The British would continue fighting in the California Peninsula until the treaty of San Diego (Jamestown) in October of 1849.


Mexico lost nearly half of its territory, mostly unpopulated at the time, leaving it with a lasting bitterness toward the British Empire and the United States. Conversely, the war also elicited the sense of national unity in Mexico, which had been lacking since the independence movement which ended in 1821.

The war also provoked the emergence of a new class of politicians in Mexico. They finally got rid of Santa Anna's grip over Mexico and eventually declared a liberal republic in 1857. Soon, laws were passed to propel the settlement of remote Mexican provinces, thereby preventing another foreign invasion.

On the other hand, the annexed territories contained thousands of Euro-Mexican and indigenous families. Some opted to return to Mexico, while others chose to remain in New Albion (having been given new provisions in the treaty of San Diego, such as double citizenship).

The U.S. government felt that, though American civilians were welcomed into the newly British lands, they had been cheated out of land that the Americans had fought for (and which had been found to be very valuable). In addition, an agreement was signed to form and independent Texas again. This sense of resentment slowly died down as many Americans became leaders of both neighboring countries.

In 1855, the U.S., U.K., and Texas signed the Continental Commerce Treaty, which helped realise both countries dream of a Transcontinental Railroad. Mexico later ratified the treaty, which eventually became NAFTA.

Andrew Westly was granted the colonial title of Earl. Soon after, Westly revealed that his real name was Andrew Curry, but refused to turn himself in. A standoff between the Earldom of Westly and the British government continued until 1970, when Robert-O'Connor renounced his title.

Through the efforts of the Dublin Colonists, the Green Army was formed, and though it is mostly a cultural organization, it continues to this day.

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